Journal of Oil Palm Research Vol. 24  2012 August p.  1421-1431

Conventional gel permeation chromatography vs. gel permeation chromatography with combined detectors

Author(s): BONNIE TAY Yen Ping* ; NURUL'AIN Hanzah*

Conventional gel permeation chromatography with a single differential refractive index detector (GPC-DRI) and GPC-DRI/viscometry were used to analyse low molecular weight compounds (palm oil and its fractions, polyether polyols, palm oleic acid-based polyols (PolyMo), palm kernel olein-based polyols and commercial palm oil polyols) and high molecular weight palm oil polyols (POP Pioneer, POP Primers Type 1, Type 2 and Type 3, and POP Premier) and commercially available palm oil polyols. The low and high molecular weight samples were analysed using PLgel Mixed E and PLgel Mixed D columns, respectively. Narrow distribution polystyrene with varying molecular weight was used as the standards for normal calibration (GPC-DRI) and universal calibration (GPC-DRI/viscometry). GPC analyses for all of the samples were carried out using tetrahydrofuran stabilised by 5% butylated hydroxytoluene (BHT) as the mobile phase. The flow rate was maintained at 1 ml min-1 with the column oven temperature at 30°C. It was found that in all of the compounds analysed, the peak average molecular weight (Mp), number average molecular weight (Mn) and weight average molecular weight (Mw) obtained using the two methods showed obvious differences. The molecular weight distributions (MWD) of palm-based polyols showed that the modality was similar, but the overlaid MWD from the two different methods showed they were not precisely matched. The results show that the use of conventional GPC with non-matching calibration standards may not give the absolute molecular weight averages and MWD. Due to the unavailability of matching commercial standards, GPC-DRI/viscometry was found to be more suitable for the analyses of palm oil-based polyols because the method relies on universal calibration.

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Author Information
* Malaysian Palm Oil Board, P. O. Box 10620, 50720 Kuala Lumpur, Malaysia.

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